Fire-resistant textile yarn and use thereof

ABSTRACT

Yarn comprising a core consisting of an inorganic filament surrounded by fibers made at least partly from aramide resin. The yarn count is between 30 and 60 tex, the weight proportion of the core is between 10 and 25%, the aramide fibers being spun around this core free from axial torsion.

The present invention relates to a fire-resistant textile yarn,comprising an inorganic filament core surrounded by fibres formed atleast in part from aramid resin, and relates further to use of thisyarn.

It has already been proposed to use these aramid fibres to produce yarnfor making a fire-resistant material. The said aramid fibres are similarin appearance to polyamide 6--6 fibres and are resistant to bending andequivalent abrasion. However, while polyamide 6--6 melts at 250° C.,aramid fibres at this temperature have a resistance to ruptureequivalent to 60% of their resistance at room temperature. Aramid fibresdo not melt, but begin to deteriorate above 370° C.

U.S. Pat. No. 4,381,639 discloses a yarn of the type comprising a core,formed from a continuous filament comprising at least 96% SiO₂,surrounded by aramid fibres, the mass ratio of fibres/core being 40:60with a core 0.5 mm in diameter. Yarn of this type is unsuitable formaking clothing fabric, but can only be used for producing protectivefabric for items of safety clothing which are only to be worn forperforming special tasks, for a limited period. The mass ratio of aramidfibres and the core is too low to ensure proper covering of the core. Asthe aramid fibres are pigmented and the filament of the core is not,this core will appear in the fabric. Although poor covering of the coreis acceptable for safety clothing for professional use only, this is notthe case when the fabric is intended for clothing which, in addition toits fire-resistant properties, is also to comprise an item of clothing,the appearance and comfort of which should be comparable to those ofordinary fabric. This is especially the case with fabrics used in makinguniforms.

It is obvious that if, in the case of the type of yarn disclosed in theaforementioned document, it were desirable to increase substantially themass ratio of aramid fibres relative to that of the core, the yarn countwould at the same time be increased and would therefore become too highfor making clothing fabric.

The thickness of the filament used to form the core of the yarn is inparticular imposed by the twisting which this filament undergoes duringthe operation to spin the aramid fibres around the core, twisting whicha substantially finer filament would not tolerate or which wouldexcessively weaken it.

It has likewise been proposed in U.S. Pat. No. 4,384,449 to manufacturea yarn with a core made from an inorganic substance around which twoaramid filaments or yarns formed from aramid fibres are wound along twocounter-directional helixes. Where the core is surrounded by aramidfibres the yarns are spun beforehand, so that the resulting yarn is atype of twister yarn formed about a core. The aramid fibres aretherefore not spun around a frame. It is obvious that a yarn of thistype can be used to produce a protective fabric, particularly for makinggloves, but would not be suitable for making clothing fabric.

It will be seen that the heat-resistant yarns proposed by the prior artcan be used to manufacture protective fabrics, but would not be used tomake fabrics suitable for clothing. Fabrics of this type should have, inaddition to their properties for protecting against heat and fire, theappearance of any other clothing fabric and adequate mechanicalresistance to stress and rupture. This fabric must obviously bepermeable to air and vapour to allow physiological exchanges to occur,and its surface unit weight should not be too great, but should becomparable to that of normal clothing fabric.

The aim of the present invention is to propose a solution combiningthese different requirements.

To this end, the subject of the invention is a heat-resistant textileyarn comprising an inorganic filament core surrounded by fibres formedat least in part from aramid resin, characterised in that the yarn countis between 30-50 tex, the mass ratio of the core being between 10% and25%, the aramid fibres being spun around this core without axialtwisting. The subject of this invention is also the use of this yarn inmaking clothing fabric, characterised in that the warp yarn count is 10%to 20% lower than the weft yarn count, the inorganic filament of thewrap yarn making up 10% to 15% of the mass of the yarn count, while theinorganic filament of the weft yarn accounts for 20% to 25% of the yarncount.

In contrast to yarns with a glass core surrounded by aramid fibres or amixture comprising at least a proportion of these fibres, spun withaxial twisting of the core, for example using the open end spinningprocess, the yarn which is the subject of the invention is provided witha core which is not axially twisted, which means that the proportion ofcore can be reduced substantially. This means that a much finer yarn canbe produced in which the core has a better covering of fibres, and meansthat a much more flexible yarn can be produced. The finer the core, themore flexible the yarn and the easier it is to conceal it with a layerof fibres. In a fire-resistant fabric formed by a conventional yarn witha glass core, it is difficult to conceal the core completely, withoutmaking a thick yarn, the core already being relatively thick on its own.Although fabric of this type is acceptable for making work clothing, itis not so for making a uniform for example, for which the appearanceshould obviously not be in any way different from that of traditionalfabric, even though special properties are required.

The manufacture of the yarn, which is the subject of the invention, witha fine non-axially twisted core, more particularly with a monofilamentis achieved by what is known as the DREF process, performed by aspinning frame made by the FEHRER company. According to this process,the fibres are wound around the core. Since the core is not subjected toaxial twisting as in the conventional spinning process, it is thereforepossible to use a glass monofilament which, for a yarn of 30 to 50 tex,makes up between 10% and 25% by weight of this yarn, i.e. a filament ofbetween approximately 50 and 80 μm.

Two different yarns have been manufactured using this principle. Thefirst is a yarn of 50 tex comprising a glass monofilament of 11 texhaving a diameter of approximately 75 μm surrounded by 50% Kermel®aramid fibres made by Rhone-Poulenc and 50% viscose fibres spun on aDREF 3 machine. The strength of this yarn is 10N, its coefficient ofvariation a % of the strength CV%R is 3.5 and its % extension is 3%.

The second of these yarns has a count of 42 tex and comprises a glassmonofilament of 5.5 tex having a diameter of approximately 50 μmsurrounded by fibres comprising 50% Kermel® aramid fibres made byRhone-Poulenc and 50% viscose fibres spun on a DREF 3 machine. Thestrength of this yarn is 6N, its coefficient of variation as a % of thestrength CV%R is 3.5 and its regain is 3%.

These two yarns were used for manufacturing a herringbone twill fabricfrom Kermel® viscose 220 with a glass core. The thicker yarn of 50 texwith a glass core of 11 tex is used as the weft yarn and appears on thereverse side of the fabric, while the finer of 42 tex with a glass coreof 5.5 tex is used as the warp yarn and thus comprises the visible partof the fabric. As a result of this combination, the thicker weft yarn,provided with a core having a diameter 50% greater than that of the warpyarn improves the strength of the fabric. However, even if the coveringof the glass core of the weft yarn is not complete, with the herringbonetwill this yarn only appears on the reverse side of the fabric.Contrastingly, the finer core of the warp yarn, where it provides theyarn with lower strength, allows better covering of the glass core andappears on the visible side of the fabric.

The fabric manufactured in this way underwent a number of tests carriedout by the Institut Textile de France. These tests were performed inaccordance with the AFNOR (French Standards Institute) standards in anormal atmosphere with relative humidity of 65% and at a temperature of20° C. The mass of the fabric per m² according to French standard NF G07104 was 225 g and permeability to air in accordance with AFNOR G 07111was tested on a TEXTEST permeability meter. The value is expressed inliters of air passing through 1 m² of fabric per second (1/m² /s) with adepression of 20 mm of water. This permeability was 458 (402-528).

The table below gives the mechanical properties of the fabric measuredin the direction of the warp and the weft. The rupture force and theextension at rupture are measured in accordance with French standard NF07119 on samples of 20×5 cm using an INSTRON 1175 electronic dynamometerwith a constant extension gradient. The induced rupture is measured inaccordance with AFNOR G 07148 using a Lhomargy rupturemeter (highcapacity active force pendulum ram impact testing machine). Thebehaviour during repeated folding was tested in order to determine theloss in rupture strength after being folded 10,000 times using an ITFLyon flexometer with rollers on which the sample is folded alternatelyin the forward direction and the reverse direction. The dynamometricmeasurement was taken in order to determine the loss in rupture strengthafter being folded 10,000 times.

                  TABLE 1                                                         ______________________________________                                                        Warp      Weft                                                ______________________________________                                        Rupture force daN                                                                              73.2 (71.4-74.4)                                                                          86.6 (80.6-90.8)                                 % Extension at rupture                                                                         13.5 (13.1-13.9)                                                                          6.9 (6.6-7.5)                                    Induced rupture daN                                                                            3.6 (3.3-3.7)                                                                             4.6 (4.3-5.0)                                    Behaviour during repeated                                                     folding                                                                       Normal fabric strength daN                                                                     73 (71.9-74.7)                                                                            83.4 (78.9-89.4)                                 after 10,000 folds daN                                                                         73.8 (71.9-75.6)                                                                          77.2 (74.5-79.3)                                 Loss in strength 0%          7.4%                                             ______________________________________                                    

This fabric also underwent inflammability tests in accordance with AFNORstandard G 07113. The table below gives the values measured using sixsamples, three warp and three weft:

                  TABLE 2                                                         ______________________________________                                        Warp   Area of the   Weft     Area of the charrad                             Samples                                                                              charred region cm.sup.2                                                                     samples  region cm.sup.2                                 ______________________________________                                        1      14            4        10                                              2      13            5        11                                              3      11            6        16                                              Average                                                                              13            Average  12                                              Overall averge: 12.5                                                          ______________________________________                                    

The same fabric underwent water-proofing and oil-proofing treatmentusing two products: a water-proofing product by Ciba-Geigy sold underthe trade name of Phobotex® FTC which is a derivative of thecondensation of formaldyehyde and an amino 1.3.5 triazine with 1 or 2NH₂ groups and an oil-proofing agent by the 3M company marketed inFrance by Ciba-Geigy under the trade name Scotchgard® FC 232.

The Kermel viscose 220 herringbone twill fabric with the glass coretreated in this way underwent surface wetting comparison tests inaccordance with the standard NF G 07056, water penetration testsaccording to standard NF G 07057 and oil penetration tests according tothe Scotchgard AATCC 118 method. To carry out this comparison aKermel/Viscose 205 herringbone twill fabric was used.

The tests were performed on two samples of fabric after treatment, andon samples which had been dry cleaned in the presence ofperchlorethylene without RB 1/10 booster for 20 mins and dried at roomtemperature.

The table below gives the results measured after the various tests. Thetable comprises three columns ST, SCHMERBER and OLEO referringrespectively to surface wetting by spray, penetration by water and theScotchgard method developed by the 3M company and accepted as auniversal reference, each of these three columns is subdivided into twocolumns EO and 1N indicating respectively the measurement taken from thefabric before cleaning and from the fabric after dry cleaning in theaforementioned conditions. For the ST and OLEO tests the figurescorrespond to performance indices 1 to 5, the last figure indicating thebest performance. With regard to the SCHMERBER test the figures indicatethe height of the water column in mm to obtain fabric penetration.

                  TABLE 3                                                         ______________________________________                                                   ST     SCHMERBER     OLEO                                                     EO   1N    EO       1N     EO   1N                                 ______________________________________                                        Grey/green KV 205                                                                          5      2     180-190                                                                              160-170                                                                              5    2                                Glass core KV 220                                                                          5      2     130-140                                                                              150-150                                                                              5    2                                ______________________________________                                    

Where it is desirable for the fabric to be able to undergo thermaltreatment in order, in particular, to remove harmful chemical productswith which it has been impregnated, it may be advantageous to replacethe glass core with a metal core in order to provide the possibility ofheating by inducing an electric current in the metal core. In the caseof steel for example with a 50 tex yarn, the maximum diameter of thefilament would be limited to 45 μm for a proportion by weight of 25%.

On the other hand, it would be possible to form filaments of B or SiC ona core of W 13 μm in diameter on which boron is deposited by thechemical decomposition of BCl₃. The same process can be used to producefilaments of W/SiC. This information is contained in the "Encyclopaediaof Chemical Technology" Kirk-Othmer, Third edition, Volume 6 page 296(John Wiley and Sons). Given the low density of the boron or the SiC itis possible to make filaments which are stronger than steel for anequivalent cross section. In that case, and so as not to exceed theproportion of 25% for yarns of 50 tex, the W/B filaments may have amaximum diameter of 75 μm and those of W/SiC 65 μm allowing for thetungsten core of 13 μm. Naturally, filaments of this type allow theproportion by weight of the core to be reduced relative to this maximumvalue whilst providing the fabric with good mechanical strength, thefilaments being able to be made to the required diameter by accretionabout the initial tungsten core of 13 μm.

We claim:
 1. A fire-resistant textile yarn comprising an inorganicfilament core surrounded by fibres formed from at least 50% by weight ofaramid resin, wherein the yarn count is between 30-50 tex, the massratio of the core being between 10% and 25%, the aramid fibres beingspun without axial twisting around this core.
 2. A textile yarnaccording to claim 1, comprising 50% aramid fibres and 50% viscosefibres.
 3. A textile yarn according to claim 1, wherein the core is amonofilament.
 4. A textile yarn according to claim 3, wherein the coreis a glass filament.
 5. A textile yarn according to claim 3, wherein thecore is a metal filament.